A liquid crystal projector that modulates illuminating light with a specified image signal using a liquid crystal display and which magnifies and projects the modulated light onto a screen is conventionally known (e.g., see Japanese Laid Open Patent Application H9-33881).
It is desirable to have the projection lens used with a liquid crystal display be approximately telecentric on the reducing side of the projection lens, as the liquid crystal display requires that the light illuminating its back side be orthogonal to the surface of the display for proper operation of the display. In the case where such a liquid crystal display is used with a projection lens that is not telecentric on the reducing side, there is unnecessary reduction in the amount of light in the periphery of the displayed image.
In recent years, color liquid crystal projectors which can accept projection lenses with different focal lengths to enable various kinds of presentations to be given have been in demand. Improvement in the image quality as well as a reduction in cost of the equipment has been desired. Further, on-axis chromatic aberration of the projection lens, resulting in deviations in the imaging position among different color components, has been a cause of image degradation using color liquid crystal projectors.
Because the reduction side of a projection lens for use with liquid crystal displays that modulate each of three color components of a color image is usually made to be approximately telecentric, on-axis chromatic aberration is commonly corrected by adjusting the distance from each liquid crystal display to the screen. If however, the projection lens is changed to one having a different focal length, the on-axis chromatic aberration occurs anew. Moreover, if the lens is changed to a telescopic lens having a long focal length, the on-axis chromatic aberration will not be tolerable in the displayed image. Although a method exists which corrects for chromatic aberration by using an abnormal dispersion glass in the projection lens, a large cost increase results when this method is used, making it difficult to satisfy the demand for reducing the cost.
In the TV camera field, a TV camera is known where a correction plate is arranged facing against a prism surface and aberrations are corrected by this correction plate (see Japanese Laid Open Patent Application 53-74319). However, in this type of TV camera optical system, the reduction side of the lens doesn't have to be approximately telecentric as in the projector apparatus of the present invention, making the concept of on-axis chromatic aberration correction completely different.